Insulating glass units commonly comprise two or more spaced, parallel glass panes, confronting surfaces of the panes being separated from one another by peripheral spacer(s). One or more of the confronting surfaces may be coated with metal oxides or other materials to improve thermal efficiency of the glass units. The spacers, which commonly are tubular lengths of metal, extend around the periphery of the glass panes and are sealed to confronting surfaces of the panes by means of relatively soft, adherent sealants.
From a structural standpoint, spacers must support pairs of glass panes with respect to one another against stresses resulting from positive or negative windload due to thunderstorms or major atmospheric disturbances and from temperature differentials in the glass panes. Organic sealants of the spacers referred to above generally are the weakest structural elements of the spacers and do not restrain glass panes from in-plane or bending movements; spacers employing organic sealants thus provide simply supported boundary conditions for the individual panes. Ceramic frit and other rigid spacers have been suggested in the prior art, and spacers of this type provide a rigid support approaching "clamped" boundary conditions. The probability of failure of glass panes under clamped boundary conditions from windload-induced stresses typically is much higher than that resulting from the use of simply supported boundary conditions, and clamped boundary conditions thus tend to require the use of thicker or tempered (and more costly) glass panes. The spacers also seal the interpane space (the space between confronting pane surfaces) from the atmosphere. The interpane space commonly contains dry air or an inert gas of low thermal conductivity, such as argon, and it is important that the interpane space be kept substantially free of moisture (which may condense) and even minute quantities of other contaminants.
In addition, spacers should be highly thermally insulative. The gas-filled interpane space offers excellent resistance to the flow of heat from an inner pane facing the interior of a building to the outer pane facing the outdoors. The bulk of the heat loss adjacent the periphery of insulating glass units occurs through the spacer because it is much more conductive to heat than is the gas in the interpane space. As a result, during wintertime conditions, the temperature of the inner pane peripheral area (usually considered to be a 21/2 inch wide strip around the periphery of the pane), especially near the bottom of the units, may fall below the dew point of air adjacent the inner pane, causing undesirable condensation. The "sightline" (the distance from the edge of the glass pane to the inner edge of the spacer) should ideally be as small as possible to maximize the vision area, and sightlines often are required to be less than 3/4 inches or even less than 1/2 inches. Thus, ideal spacers should allow the glass panes to bend while yet retaining excellent insulating qualities and resistance to gas transmission; yet, the spacers themselves should not unduly limit the viewing area.
To reduce the severity of the problems referred to above, various spacer designs have been investigated. There is yet a substantial and unfilled need for a durable spacer which provides reliable structural support between pairs of glass panes, which is substantially impermeable to moisture and gases, and which yet is highly insulative so as to strongly resist the flow of heat through the spacer from one pane to another.